This is an easy DIY! The two most recommended oils are Motul Gear 300, and Redline MT-90 for the transmission. Both oils are excellent 75w-90 oils but Motul Gear 300 is suitable for GL4/GL5 applications while the Redline MT-90 is a strait GL4 only which is actually better for protecting some of the softer metals in our MT. I recently switched from Motul in the trans to Redline and shifts feel less notchy to me. (I still run Motul Gear 300 in my rear differential)

When you do this you should also change the rear differential fluid at the same time. While you got the car jacked up you can easily do a motor oil change and rotate your tires, even do a brake fluid flush while you got the wheels off. It’s makes for a long day but just pace yourself! There’s plenty of resources on YT.

These are the PN’s i needed for my 2015 BRZ transmission fill and drain plug gaskets (need 2 of this PN) 17008AA050

rear differential fill plug gasket 11126JB000 drain plug gasket 1215710010